In a transportation system such as a railroad, a monorail or the like causing an electric railcar to travel by a direct-current feeding method, when a direct-current substation being the power supply source fails, the electric railcar that cannot receive power any longer becomes unable to travel in some case. Hence, to secure the power supply for traveling in the case of power failure or the like, there is suggested a technology of mounting a power storage device on the electric railcar so that the electric railcar travels by the power of the power storage device.
On the other hand, a technology of providing a power storage device on a feeder line side so as to move the electric railcar to the nearest station by supplying power from the power storage device to the feeder line when the alternating-current power supply cannot be obtained any longer, has been already practically used.
However, in the case of the former technology of mounting the power storage device on the electric railcar, the electric railcar of the monorail or the like cannot be said to have space enough to mount the power storage device thereon. Further, mounting the power storage device being a high-energy body on the electric railcar results in an increased risk such as fire. In particular, in the transportation system such as the monorail, there also occurs a risk of parts falling after reconstruction work for mounting the power storage device.
Further, in the case of the latter technology of providing the power storage device on the feeder line side, for example, a power storage device of an overhead contact line direct-coupled type generally needs to have a larger number of cells in series, resulting in an increase in size of the whole power storage device and in cost. Further, in consideration of the voltage drop in the feeder line, movement of vehicle for a long distance is difficult.
Note that in the case of a power storage device not of the overhead contact line direct-coupled type but of supplying power to the feeder line side via a converter, more power is consumed due to switching loss of the converter. Accordingly, the power storage device in this case quickly decreases in charge amount, and therefore it is impossible to obtain sufficient supply of power at power failure or the like. Hence, it is conceivable to make the power storage device have a large capacity, but there occurs problem in terms of cost because of the need to arrange many power storage devices with large capacity in a distributed manner.
Here, especially when the electric railcar of the monorail type stops between stations, it is extremely difficult, for example, for passengers to walk to escape to the near station. Therefore, a further improvement in the power feeding technology is required also in terms of safety.